Not applicable.
1. Field of the Invention
The invention relates to footwear and, more particularly, to footwear constructed to dissipate electrostatic charges.
2. Description of the Invention Background
Static electricity is the accumulation of electric charge in an insulated body, most frequently caused by friction, but also by other means, such as induction etc. Electrostatic discharge (ESD) is the transfer of electric charge between two bodies, often accompanied by a visible spark, as in the familiar phenomenon of doorknob shock. While electrostatic discharge per se may not be immediately harmful to a human body, at least at level of voltage less than about 3000 volts, a discharge of much smaller voltage might be damaging to sensitive equipment, such as electronic components for computers and magnetic data carriers. A low volt electrostatic discharge may also ignite explosive gases. Accordingly, protection against ESD is required in the electronics and telecommunications industries and in other industries wherein sensitive electrical components or explosive materials are being handled.
ESD is of particular concern to the electronics industries. For example, if a quality control inspector carries a static charge during an inspection or testing operation, at a minimum, the accuracy of the test may be affected or, in worse cases, one or more sensitive components may be damaged. One method commonly employed to address this problem is the use of conductive footwear. By wearing a pair of conductive shoes, the person testing the electronic products is electrically grounded and the static charge is therefore eliminated. Various tests have shown that conductivity, more specifically, the impedance of a conductive shoe must be maintained within a certain range. One company in the computer and electronics industry recommends that the impedance of a conductive shoe be maintained within 106 ohms to 107 ohms. Other forms of grounding have been used to dissipate the electrostatic charge before it builds up to harmful levels. Such grounding measures include installing conductive or dissipative floors or stepping mats and/or wearing conductive wrist straps.
The efficacy of antistatic devices such as footwear, wrist and heel straps, etc. is typically determined by the electrical resistance of the conducting surface of the device in ohms. This electrical resistance may be affected by various environmental factors, such as humidity, dirt and other contamination, wear and other damage. A variable or unreliable electrical resistance does not provide continuous and reliable protection, as required in many environments with components sensitive to relatively small electrostatic discharges.
There remains, therefore, a need for footwear with improved electrostatic discharge properties that overcomes the limitations, shortcomings and disadvantages of the previous approaches.
The invention meets the identified needs, as well as other needs, as will be more fully understood following a review of this specification and drawings.
One embodiment of the invention comprises an electrostatic circuit for a sole having a conductive outsole, a conductive insole and a nonconductive midsole positioned between the insole and outsole. This embodiment of the electrostatic circuit includes a first substrate that has a first end and a second end. In one embodiment, the substrate is flexible and in another embodiment, the substrate may be relatively rigid and inflexible. The electrostatic circuit may further include at least one conductor path that is attached to the first substrate. Each conductor path has a first exposed end that is adjacent to the first end of the first substrate and that is attachable to the conductive outsole. Each conductor path also has a second exposed end that is adjacent to the second end of the substrate and that is attachable to the conductive insole. In addition, the circuit includes at least one resistor that is electrically coupled to each conductor path and mounted to the first substrate. In alternative embodiments, each end of the conductive paths may be attached to a corresponding conductive pad to provide an enlarged area for affixing the conductive path to the other components of the sole.
Another embodiment of the present invention includes an electrostatic circuit for a sole that has a conductive outsole, a conductive insole and a nonconductive midsole between the insole and outsole. In this embodiment, the electrostatic circuit includes a first substrate that has a first end and a second end. A first conductor path is attached to the first substrate. The first conductor path has a first exposed end that is adjacent to the first end of the first substrate and that is attachable to the conductive outsole. The first conductor path also has a second exposed end that is adjacent to the second end of the first substrate and that is attachable to the conductive insole. A first resistor is supported on the first substrate and is electrically coupled to the first conductor path. In addition, a second conductor path is attached to the first substrate. The second conductor path has a second exposed end that is adjacent to the first end of the first substrate and that is attachable to the conductive outsole. The second conductor path also has a second exposed end that is adjacent to the second end of the first substrate and that is attachable to the conductive insole. A second resistor is supported on the first substrate and is electrically coupled to the second conductor path. A third conductor path is attached to the first substrate. The third conductor path has a first exposed end that is adjacent to the first end of the first substrate and is attachable to the conductive outsole. The third conductive path also has a second exposed end that is adjacent to the second end of the substrate and that is attachable to the conductive insole. A third resistor is supported on the first substrate and is electrically coupled to the third conductor path.
Another embodiment of the present invention comprises a sole for a conductive shoe. The sole includes a conductive outsole and a midsole that is adjacent to the outsole. A conductive insole is adjacent to the midsole. The sole further includes a printed circuit that comprises a first substrate and at least one conductor path that is attached to the first substrate. Each conductor path has a first end that is attached to the conductive outsole and a second end that is attached to the conductive insole. At least one resistor is electrically coupled to each conductor path and mounted to the first substrate.
Yet another embodiment of the present invention comprises a method for applying a desired amount of electrical impendence to an electrostatic current passing through a shoe having a conductive outsole, a conductive insole and a nonconductive midsole between the outsole and insole. The method includes affixing one end of a first conductive path formed on a substrate to the conductive outsole and electrically coupling a first resistor having the desired amount of impedance to the conductive path. The method further includes affixing another end of the first conductive path to the conductive insole.
Another embodiment of the present invention comprises a method of manufacturing a sole for a conductive shoe. The method includes affixing a first conductive path to a substrate such that the first conductive path has a first exposed end and a second exposed end and attaching a first resistor to the first conductive path. The method also includes forming a conductive outsole and a nonelectrically conductive midsole and supporting the nonelectrically conductive midsole on the electrically conductive outsole. The method further includes forming an electrically conductive insole and supporting the electrically conductive insole to the nonelectrically conductive midsole. The substrate is supported within the midsole such that the first exposed end of the first conductive path is in electrical contact with the electrically conductive outsole and the second end of the first electrically conductive path is in electrical contact with the electrically conductive insole.
Other features and advantages of the invention will become apparent from the detailed description of the embodiments set forth herein and from the appended claims.